Image forming apparatus

ABSTRACT

An image forming apparatus comprising: an image forming unit configured to form an image on a recording medium based on an image forming condition; an image reader configured to read an image for adjustment of the image forming condition, which is formed on the recording medium; and a controller configured to: control the image forming unit to form images for adjustment; control the image reader to read the images for adjustment; determine a target data based on a reading result of a first image included in reading results of the images for adjustment; and adjust the image forming condition, during execution of a job in which the image forming unit forms a plurality of images on a plurality of recording mediums, based on the target data and a reading result of second image included in the reading results of the images for adjustment.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to an image forming apparatus, such as aprinter, a copying machine, a facsimile machine, or a multifunctionapparatus.

Description of the Related Art

An image forming apparatus performs processing for improving stabilityof image quality, for example, after the end of warm-up at startup. Forexample, the image forming apparatus forms, as an image for adjustment,a specific pattern such as a tone pattern on a recording medium such aspaper, and reads the specific pattern by an image reading apparatus suchas a scanner. The image forming apparatus stabilizes the image qualityby feeding back information based on the read specific pattern to imageforming conditions including a γ correction value. In the image formingapparatus, tone correction is performed by correcting the image formingconditions so that tone characteristics of the image forming apparatusmatches target tone characteristics.

In United States Patent Application Publication No. 2011/0222869 A1,there is disclosed an image forming apparatus in which a belt-shapedpattern having a specific tone and a predetermined length in a mainscanning direction is formed on a recording medium, and a feedbackcontrol is performed based on results of reading the belt-shaped patternat a plurality of positions, to thereby suppress density unevenness inthe main scanning direction.

In a case where printing is continuously performed on a plurality ofsheets of recording media in one job, it is required to maintain theuniformity of the image densities of respective images formed on theplurality of sheets of recording media. In such a case, for example, theimage forming apparatus determines a target tone at the start of a job,and periodically corrects a difference from the target tone duringexecution of the job. Specifically, the image forming apparatus prints atone pattern on a recording medium at the start of a job to create achart for adjustment. The image forming apparatus determines a targettone based on a reading result of the tone pattern printed on the chartfor adjustment. The image forming apparatus corrects a change in imagedensity due to changes in the internal state (for example, a change indevelopment characteristics due to toner replenishment and a change intransfer characteristics due to changes in temperature and humidity)caused by continuous printing. To that end, the image forming apparatuscreates a chart for adjustment each time printing has been performed ona fixed number of sheets of recording media, and corrects image formingconditions based on a difference between a reading result of the tonepattern read from the chart for adjustment and the target tone. Thus,the image density is corrected, and the image densities of the pluralityof sheets of recording media are maintained to be uniform.

However, the reading of the tone pattern may fail due to, for example,misalignment of the tone pattern due to poor conveyance of the recordingmedium or a failure of the image reading apparatus. In a case where thereading of the tone pattern fails at a stage of determining the targettone at the start of the job, the image forming apparatus cannotdetermine the target tone. In that case, when the reading of the tonepattern at a printing interval of a fixed number of sheets issuccessful, the target tone can be determined. However, the fixednumber, which corresponds to the printing interval, of sheets ofrecording media counted from the first sheet are not subjected to imagedensity correction because the target tone has not been determined.Therefore, it is difficult to maintain the image quality of therecording medium during this period. In addition, the reading of thetone pattern may fail during the image density correction which isperformed during the job. In this case, when a chart for adjustment iscreated and read again, productivity decreases. In view of theabove-mentioned problems, the present disclosure has an object toprovide an image forming apparatus capable of maintaining image qualitywhile suppressing a decrease in productivity.

SUMMARY OF THE INVENTION

An image forming apparatus according to the present disclosure includes:an image forming unit configured to form an image on a recording mediumbased on an image forming condition; an image reader configured to readan image for adjustment of the image forming condition, which is formedon the recording medium; and a controller configured to: control theimage forming unit to form images for adjustment; control the imagereader to read the images for adjustment; determine a target data basedon a reading result of a first image included in reading results of theimages for adjustment; adjust the image forming condition, duringexecution of a job in which the image forming unit forms a plurality ofimages on a plurality of recording mediums, based on the target data anda reading result of second image included in the reading results of theimages for adjustment; control the image forming unit to form the firstimage again during execution of the job, in a case where the imagereader fails to read the first image during execution of the job; andavoid adjust the image forming condition based on the reading result ofthe second image during execution of the job, in a case where the imagereader fails to read the second image during execution of the job.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of an image processing system.

FIG. 2 is a system configuration diagram for illustrating how to controloperations of the image processing system.

FIG. 3 is a configuration diagram of an image forming apparatus.

FIG. 4 is an explanatory view of CISs.

FIG. 5 is an exemplary view of a chart for adjustment.

FIG. 6 is a four-quadrant chart for showing how a tone is reproduced.

FIG. 7A, FIG. 7B, FIG. 7C, and FIG. 7D are exemplary views of a settingscreen.

FIG. 8 is a flow chart for illustrating printing processing includingcorrection processing for an image density.

FIG. 9 is a flow chart for illustrating the printing processingincluding the correction processing for the image density.

FIG. 10 is a flow chart for illustrating the printing processingincluding the correction processing for the image density.

DESCRIPTION OF THE EMBODIMENTS

Now, an embodiment of the present disclosure is described in detail withreference to the accompanying drawings.

<Image Processing System>

FIG. 1 is a configuration diagram of an image processing systemincluding an image forming apparatus according to this embodiment. Theimage processing system includes an image forming apparatus 101 and anexternal controller 102. Examples of the image forming apparatus 101include a multifunction apparatus and a multifunction peripheral (MFP).Examples of the external controller 102 include an image processingcontroller, a digital front end (DFE), and a print server.

The image forming apparatus 101 and the external controller 102 areconnected to each other so as to enable communication therebetweenthrough an internal local area network (LAN) 105 and a video cable 106.The external controller 102 is connected to a client personal computer(PC) 103 through an external LAN 104. The external controller 102obtains a print instruction (print job) from the client PC 103.

A printer driver having a function of converting an image into a printdescription language that can be processed by the external controller102 is installed on the client PC 103. A user can instruct printingthrough the printer driver by various applications. The printer drivertransmits image data to the external controller 102 based on a jobinstructed from the user. The external controller 102 receives a printjob including the image data from the client PC 103, performs dataanalysis and rasterization processing, and instructs the image formingapparatus 101 to print (to perform image formation) based on the imagedata.

The image forming apparatus 101 is configured by connecting a pluralityof apparatus having different functions including a printing apparatus107 to one another, and can perform complicated printing processingincluding bookbinding. The image forming apparatus 101 according to thisembodiment includes the printing apparatus 107 and a finisher 109. Theprinting apparatus 107 forms an image on a recording medium fed from asheet feeder provided at a lower part of a main body, through use of adeveloper (for example, toner). The printing apparatus 107 forms yellow(Y), magenta (M), cyan (C), and black (K) images. A full-color image inwhich the images in the respective colors are superimposed on oneanother is formed on the recording medium. The recording medium havingthe image formed thereon is conveyed from the printing apparatus 107 tothe finisher 109. The finisher 109 stacks such recording media havingimages formed thereon onto a stack tray 332.

This image processing system is configured by connecting the externalcontroller 102 to the image forming apparatus 101, but the externalcontroller 102 is not always required. For example, the image formingapparatus 101 may be configured to obtain the print job including theimage data directly from the client PC 103 through the external LAN 104.In this case, the image forming apparatus 101 is configured to performthe data analysis and rasterization processing that are supposed to beperformed by the external controller 102. That is, the image formingapparatus 101 and the external controller 102 may be integrallyconfigured.

<System Configuration>

FIG. 2 is a system configuration diagram for illustrating how to controloperations of the image processing system. In this case, a systemconfiguration of each of the image forming apparatus 101, the externalcontroller 102, and the client PC 103 is described.

Printing Apparatus

The printing apparatus 107 includes a communication interface (I/F) 217,a LAN I/F 218, and a video I/F 220 in order to communicate to/from otherapparatus. The printing apparatus 107 includes a central processing unit(CPU) 222, a memory 223, a storage 221, an image reader 241, and a jobanalyzer 226 in order to control operations of the printing apparatus107. The printing apparatus 107 includes an exposure device 227, animager 228, a fixer 229, and a sheet feeder 230 in order to form animage. The printing apparatus 107 includes an operating device 224 and adisplay 225 as user interfaces. Those components are connected to oneanother through a system bus 231 so as to enable communication to/fromone another.

The communication I/F 217 is connected to the finisher 109 through acommunication cable 279, and controls communication to/from the finisher109. In a case where the printing apparatus 107 and the finisher 109operate in cooperation with each other, information and data aretransmitted and received through intermediation of the communication I/F217. The LAN I/F 218 is connected to the external controller 102 throughthe internal LAN 105, and controls communication to/from the externalcontroller 102. The printing apparatus 107 receives a print setting andimage data from the external controller 102 through intermediation ofthe LAN I/F 218. The video I/F 220 is connected to the externalcontroller 102 through the video cable 106, and controls communicationto/from the external controller 102. The printing apparatus 107 receivesimage data representing an image to be printed from the externalcontroller 102 through intermediation of the video I/F 220.

The CPU 222 executes computer programs stored in the storage 221 tocomprehensively control image processing and image forming processing(printing control). The memory 223 provides a work area for the CPU 222to execute various kinds of processing. In a case of performing imageforming processing, the CPU 222 controls the exposure device 227, theimager 228, the fixer 229, and the sheet feeder 230.

The exposure device 227 includes a photosensitive member, a chargingwire which charges the photosensitive member, and a light source whichexposes the photosensitive member to light in order to form anelectrostatic latent image on the photosensitive member. Thephotosensitive member is, for example, a photosensitive belt having aphotosensitive layer formed on a surface of a belt-like elastic memberor a photosensitive drum having a photosensitive layer formed on asurface of a cylinder. In place of the charging wire, a charging rollermay be used. The exposure device 227 charges a surface of thephotosensitive member to a uniform negative potential through use of thecharging wire. The exposure device 227 outputs laser light from thelight source based on the image data. The laser light is scanned acrossthe surface of the photosensitive member that has been uniformlycharged. Thus, a potential of the photosensitive member changes at aposition irradiated with the laser light, and an electrostatic latentimage is formed on the surface of the photosensitive member. Fourphotosensitive members are provided in correspondence with the fourcolors of yellow (Y), magenta (M), cyan (C), and black (K).Electrostatic latent images corresponding to images in mutuallydifferent colors are formed on the four photosensitive members.

The imager 228 transfers a toner image formed on the photosensitivemember onto the recording medium. The imager 228 includes a developingdevice, a transfer unit, and a toner replenisher. The developing deviceforms a toner image by causing toner charged to a negative polarity toadhere from a developing cylinder to an electrostatic latent imageformed on the surface of the photosensitive member. Four developingdevices are provided in correspondence with the four colors of yellow(Y), magenta (M), cyan (C), and black (K). The developing devicevisualizes the electrostatic latent image on the photosensitive memberthrough use of the toner of the corresponding color. In a case where anamount of toner inside the developing device is insufficient due to theformation of the toner image, the developing device is replenished withtoner by the toner replenisher.

The transfer unit includes an intermediate transfer belt, and transfersthe toner image from each of the photosensitive members onto theintermediate transfer belt. A primary transfer roller is provided at aposition opposed to each photosensitive member across the intermediatetransfer belt. In a case where a positive potential is applied to eachprimary transfer roller, the toner images are transferred from the fourphotosensitive members onto the intermediate transfer belt while beingsuperimposed on one another. Thus, a full-color toner image is formed onthe intermediate transfer belt. The toner image formed on theintermediate transfer belt is transferred onto the recording medium by asecondary transfer roller described later. The secondary transfer rollertransfers the full-color toner image from the intermediate transfer beltonto the recording medium in a case where a positive potential isapplied to the secondary transfer roller.

The fixer 229 fixes the transferred toner image to the recording medium.The fixer 229 includes a heater and a roller pair. The fixer 229 heatsand pressurizes the toner image on the recording medium by the heaterand the roller pair to melt the toner image and fix the toner image tothe recording medium. Thus, the image is formed on the recording medium.The sheet feeder 230 includes a conveyance roller and various sensors ina conveyance path, and controls a feeding operation of the recordingmedium.

The image reader 241 reads the image formed on the conveyed recordingmedium based on an instruction received from the CPU 222. For example,in a case of adjusting image forming conditions, the CPU 222 causes theimage reader 241 to read images for adjustment of the image formingconditions, which are formed on the recording medium. The job analyzer226 analyzes setting information on the image forming apparatus 101 andprint data received from the external controller 102. The operatingdevice 224 is an input device which receives input of various settingsand operation instructions from the user. Examples of the operatingdevice 224 include various input keys and a touch panel. The display 225is an output device which displays the setting information on the imageforming apparatus 101 and a processing status (status information) ofthe print job.

Finisher

The finisher 109 is, for example, a large-capacity stacker. The finisher109 includes a communication I/F 271, a CPU 272, a memory 273, and asheet delivery controller 274. Those components are connected to oneanother through a system bus 275 so as to enable communication to/fromone another. The communication I/F 271 is connected to the printingapparatus 107 through the communication cable 279, and controlscommunication to/from the printing apparatus 107. In a case where thefinisher 109 and the printing apparatus 107 operate in cooperation witheach other, information and data are transmitted and received throughintermediation of the communication I/F 271. The CPU 272 executescontrol programs stored in the memory 273 to perform various kinds ofcontrol required for sheet delivery. The memory 273 stores the controlprograms. The memory 273 provides a work area for the CPU 272 to executevarious types of processing. The sheet delivery controller 274 deliversthe conveyed recording medium onto the stack tray 332 based on aninstruction received from the CPU 272.

External Controller

The external controller 102 includes a LAN I/F 213, a LAN I/F 214, and avideo I/F 215 in order to communicate to/from other apparatus. Theexternal controller 102 includes a CPU 208, a memory 209, and a storage210 in order to control the operation of the external controller 102.The external controller 102 includes a keyboard 211 and a display 212 asuser interfaces. Those components are connected to one another through asystem bus 216 so as to enable communication to/from one another.

The LAN I/F 213 is connected to the client PC 103 through the externalLAN 104, and controls communication to/from the client PC 103. Theexternal controller 102 obtains the print job from the client PC 103through intermediation of the LAN I/F 213. The LAN I/F 214 is connectedto the printing apparatus 107 through the internal LAN 105, and controlscommunication to/from the printing apparatus 107. The externalcontroller 102 transmits, for example, the print setting and the imagedata to the printing apparatus 107 through intermediation of the LAN I/F214. The video I/F 215 is connected to the printing apparatus 107through the video cable 106, and controls communication to/from theprinting apparatus 107. The external controller 102 transmits the imagedata to the printing apparatus 107 through intermediation of the videoI/F 215.

The CPU 208 executes computer programs stored in the storage 210 tocomprehensively perform processing, such as reception of the image datatransmitted from the client PC 103, RIP processing, and transmission ofthe image data to the image forming apparatus 101. The memory 209provides a work area for the CPU 208 to execute various kinds ofprocessing. The keyboard 211 is an input device which receives input ofvarious settings and operation instructions from the user. The display212 is an output device which displays information on an executionapplication of the external controller 102 as a still image or a movingimage.

Client PC

The client PC 103 includes a CPU 201, a memory 202, a storage 203, akeyboard 204, a display 205, and a LAN I/F 206. Those components areconnected to one another through a system bus 207 so as to enablecommunication to/from one another.

The CPU 201 executes computer programs stored in the storage 203 tocontrol the operation of the client PC 103. In this embodiment, the CPU201 creates image data and transmits a print job. The memory 202provides a work area for the CPU 201 to execute various kinds ofprocessing. The keyboard 204 and the display 205 are user interfaces.The keyboard 204 is an input device which receives instructions from theuser. The display 205 is an output device which displays information onan execution application of the client PC 103 as a still image or amoving image. The LAN I/F 206 is connected to the external controller102 through the external LAN 104, and controls communication to/from theexternal controller 102. The client PC 103 transmits the print job tothe external controller 102 through the LAN I/F 206.

The external controller 102 and the image forming apparatus 101 areconnected through the internal LAN 105 and the video cable 106, but maybe connected, for example, only through a video cable as long as datarequired for printing can be transmitted and received therebetween. Itsuffices that each of the memory 202, the memory 209, the memory 223,and the memory 273 is a storage device for holding data and programs. Asthose memories, it is possible to use, for example, a volatile randomaccess memory (RAM), a non-volatile read only memory (ROM), a storage,and a universal serial bus (USB) memory.

<Configuration of Image Forming Apparatus>

FIG. 3 is a configuration diagram of the image forming apparatus 101.The display 225 is provided at an upper part of a casing of the printingapparatus 107. The display 225 displays information for a printingstatus and settings of the image forming apparatus 101. The recordingmedium having the image formed thereon by the printing apparatus 107 isconveyed to the finisher 109 provided in the subsequent stage.

The printing apparatus 107 includes, as the sheet feeder 230, aplurality of sheet feeding decks 301 and 302, conveyance paths 303, 312,314, 315, and 323, a reverse path 316, a double-sided conveyance path317, a downstream conveyance path 325, a delivery path 326, and variousrollers. Mutually different types of recording media can be stored inthe sheet feeding decks 301 and 302. Of the recording media stored inthe sheet feeding decks 301 and 302, an uppermost sheet is separated andfed to the conveyance path 303. The printing apparatus 107 includes, asthe exposure device 227, image forming units 304, 305, 306, and 307 forforming an image. The printing apparatus 107 forms a color image. Tothat end, the image forming unit 304 forms a black (K) image (tonerimage). The image forming unit 305 forms a cyan (C) image (toner image).The image forming unit 306 forms a magenta (M) image (toner image). Theimage forming unit 307 forms a yellow (Y) image (toner image).

The printing apparatus 107 includes, as the imager 228, a secondarytransfer roller 309 and an intermediate transfer belt 308 onto which thetoner images are to be transferred from the image forming units 304,305, 306, and 307. The intermediate transfer belt 308 is rotatedclockwise in FIG. 3 , and the toner images are superimposed on oneanother and transferred in the order of the image forming unit 307, theimage forming unit 306, the image forming unit 305, and the imageforming unit 304 (primary transfer). Thus, a full-color toner image isformed on the intermediate transfer belt 308. The intermediate transferbelt 308 is rotated, to thereby carry the toner image to the secondarytransfer roller 309. The recording medium is conveyed to the conveyancepath 303 at a timing at which the toner image is carried to thesecondary transfer roller 309. The secondary transfer roller 309transfers the toner image on the intermediate transfer belt 308 onto theconveyed recording medium (secondary transfer).

The printing apparatus 107 includes, as the fixer 229, a first fixingdevice 311 and a second fixing device 313. The first fixing device 311and the second fixing device 313 have the same configuration, and areeach fix the toner image to the recording medium. To that end, the firstfixing device 311 and the second fixing device 313 each include apressure roller and a heating roller. The recording medium is heated andpressurized by passing between the pressure roller and the heatingroller to have the toner image melted and press-fixed. The recordingmedium that has passed through the second fixing device 313 is conveyedto the conveyance path 314. The second fixing device 313 is arrangeddownstream of the first fixing device 311 in a conveying direction ofthe recording medium, and is used for adding a gloss to the image on therecording medium, which has been subjected to fixing processing by thefirst fixing device 311, and for ensuring fixability. For that reason,the second fixing device 313 may not be used depending on the type ofrecording medium and the content of the print job. The conveyance path312 is provided in order to convey the recording medium subjected to thefixing processing by the first fixing device 311 without passing therecording medium through the second fixing device 313.

At a position after the conveyance path 314 and the conveyance path 312merge, the conveyance path 315 and the reverse path 316 are provided. Ina case where duplex printing is instructed, the recording medium isconveyed to the reverse path 316. The recording medium conveyed to thereverse path 316 is reversed in the reverse path 316 in terms of theconveying direction, and conveyed to the double-sided conveyance path317. A surface (first surface) of the recording medium on which an imagehas been formed is reversed by the reverse path 316 and the double-sidedconveyance path 317. The recording medium is conveyed to the conveyancepath 303 by the double-sided conveyance path 317, and passes through thesecondary transfer roller 309 and the fixer 229, to thereby have animage formed on a second surface of the recording medium.

In a case of single-sided printing or in a case where images are formedon both sides by duplex printing, the recording medium is conveyed tothe conveyance path 315. The conveyance path 323 is arranged downstreamof the conveyance path 315 in the conveying direction of the recordingmedium.

As the image reader 241, contact image sensors (CISs) 321 and 322 arearranged in the conveyance path 323 so as to be opposed to each otheracross the conveyance path 323. FIG. 4 is an explanatory view of theCISs 321 and 322. The CIS 321 is an optical sensor which reads an imageon an upper surface of the recording medium being conveyed along theconveyance path 323. The CIS 322 is an optical sensor which reads animage on a lower surface of the recording medium being conveyed alongthe conveyance path 323.

The CIS 321 includes a light emitting diode (LED) 350 serving as a lightsource and a reading sensor 351 serving as a light receiver. The LED 350irradiates the upper surface of the recording medium with light at atiming at which the recording medium conveyed along the conveyance path323 reaches a reading position. The reading sensor 351 includes aplurality of light-receiving elements (photoelectric conversionelements) in a direction perpendicular to the conveying direction of therecording medium. Therefore, the direction perpendicular to theconveying direction of the recording medium is a main scanning directionof the CIS 321. The reading sensor 351 receives the light reflected bythe recording medium through the light-receiving elements. The pluralityof light-receiving elements of the reading sensor 351 each output anoutput value (electric signal) based on intensity of the reflected lightthat has been received. Each output value (electric signal) output fromthe plurality of light-receiving elements is transmitted to the CPU 222.In this manner, an image formed on the recording medium is read.

The CIS 322 includes an LED 352 and a reading sensor 353 having the sameconfigurations as those of the CIS 321. The CIS 322 operates in the samemanner as the CIS 321 to read an image formed on the lower surface ofthe recording medium at a timing at which the recording medium conveyedalong the conveyance path 323 reaches a reading position. In addition tothe CISs 321 and 322, the image reader 241 can also be implemented by aCCD or CMOS sensor.

The printing apparatus 107 in this embodiment can form images foradjustment for adjusting the image forming conditions on both sides ofthe recording medium. A recording medium having the images foradjustment formed thereon is referred to as “chart for adjustment.” Theprinting apparatus 107 prints the images for adjustment on a recordingmedium to create a chart for adjustment, and causes the CIS 321 and theCIS 322 to read the images for adjustment. Results of reading the chartfor adjustment by the CIS 321 and the CIS 322 are stored in the memory223. The CPU 222 refers to the memory 223 to analyze the results ofreading the chart for adjustment by the CIS 321 and the CIS 322, andfeeds back the analyzed results to the image forming conditions toadjust the image forming conditions.

For example, in a case where the in-machine temperature of the printingapparatus 107 rises, the image density of the image formed on therecording medium vary more greatly than when the in-machine temperatureof the printing apparatus 107 is lower. The printing apparatus 107creates a chart for adjustment, and detects the image density of theimage for adjustment based on the reading results obtained by the CISs321 and 322. The CPU 222 obtains a variation amount of the detectedimage density with respect to a target image density, and adjusts theimage forming conditions based on the variation amount. The CPU 222converts the image data based on the image forming conditions. Theprinting apparatus 107 forms an image on the recording medium based onthe image data converted by the CPU 222, to thereby control the imagedensity of the image formed on the recording medium. Thus, the printingapparatus 107 can suppress variations in the image density of the imagecaused by variations in the in-machine temperature.

For example, the printing apparatus 107 controls light emissionintensity of the light source of the exposure device 227 based on theadjusted image forming conditions, to thereby adjust the image densityto the target image density. In another case, the CPU 222 generates aone-dimensional tone correction table for suppressing the variations inthe image density based on the reading result obtained by the CIS 321(or the CIS 322). The CPU 222 converts the image data based on the tonecorrection table. The printing apparatus 107 forms an image on therecording medium based on the image data converted by the CPU 222, tothereby adjust the image density of the printing apparatus 107 to anideal image density.

The image for adjustment to be formed on the chart for adjustment may benot only an image for detecting an image density but also an image fordetecting geometric characteristics of an image or an image fordetecting color misregistration. The geometric characteristics of theimage refer to, for example, squareness and a printing position of theimage on the recording medium. In a case where the image for adjustmentfor detecting the geometric characteristics of the image is formed, theCPU 222 adjusts the image forming conditions in order to suppressvariations in the geometric characteristics based on the reading resultsobtained by the CIS 321 (or CIS 322). The CPU 222 controls, for example,a light emission timing of the light source of the exposure device 227based on the image forming conditions, to thereby adjust the geometriccharacteristics of the image to ideal geometric characteristics.

Further, in a case where an image for adjustment for detecting the colormisregistration is formed, the CPU 222 detects the color misregistrationbased on the reading results obtained by the CIS 321 (or the CIS 322).The CPU 222 adjusts the image forming conditions based on the detectedcolor misregistration in order to suppress the color misregistration.The CPU 222 controls, based on the image forming conditions, a positionof an image to be formed on each photosensitive member by the exposuredevice 227, to thereby correct the color misregistration.

The chart for adjustment is excluded so as to avoid being mixed inprinted products corresponding to the print job. To that end, theprinting apparatus 107 includes a flapper 324, the delivery path 326, aconveyance sensor 327, and a delivery tray 328. The chart for adjustmentwhich has the image for adjustment read by the CISs 321 and 322 isconveyed to the delivery path 326 by the flapper 324. The recordingmedium conveyed to the delivery path 326 is delivered to the deliverytray 328.

In a case where the recording medium is not a chart for adjustment, therecording medium is conveyed from the conveyance path 323 to adownstream conveyance path 325 by the flapper 324. A recording mediumconveyed to the downstream conveyance path 325 is passed over to thefinisher 109. In a case where the printing apparatus 107 obtains anotification of occurrence of a conveyance jam from the finisher 109,irrespective of whether or not the recording medium is a chart foradjustment, the printing apparatus 107 switches the flapper 324 towardthe delivery path 326 to deliver all the recording media in the machine(residual sheets) to the delivery tray 328. The delivery of the residualsheets to the delivery tray 328 reduces a load on the user in jamclearance.

The finisher 109 can stack the recording media passed over from theprinting apparatus 107. The finisher 109 includes a conveyance path 331and the stack tray 332 for stacking the recording media. The conveyancepath 331 is provided with conveyance sensors 333, 334, 335, and 336. Therecording media conveyed from the printing apparatus 107 are stacked onthe stack tray 332 through the conveyance path 331. The conveyancesensors 333, 334, 335, and 336 each detect passage of the recordingmedium being conveyed along the conveyance path 331. In a case where aleading edge or a trailing edge of the recording medium in the conveyingdirection is not detected by the conveyance sensors 333, 334, 335, and336 even after a lapse of a predetermined time period since start of theconveyance of the recording medium, the CPU 272 determines that aconveyance jam (conveyance abnormality) has occurred in the finisher109. In this case, the CPU 272 notifies the printing apparatus 107 thata conveyance jam has occurred.

<Images for Adjustment>

FIG. 5 is an exemplary view of the chart for adjustment. This chart 500for adjustment is conveyed in a longitudinal direction of the chart 500for adjustment. Patterns 501 for adjustment are images for adjustmentfor image density correction, and are formed on one surface of therecording medium for respective colors. The patterns 501 for adjustmentmay be formed at any positions in a peripheral edge portion of therecording medium. In this embodiment, the patterns 501 for adjustmentare formed in both end portions of the recording medium in a direction(short-side direction of the recording medium) perpendicular to theconveying direction of the recording medium. That is, the patterns 501for adjustment of two colors are formed in one end portion of therecording medium in the short-side direction, and the patterns 501 foradjustment of the remaining two colors are formed in the other endportion of the recording medium in the short-side direction. In thisembodiment, patterns 501C and 501M for adjustment of cyan and magentaare formed in one end portion of the recording medium in the short-sidedirection, and patterns 501Y and 501K for adjustment of yellow and blackare formed in the other end portion of the recording medium in theshort-side direction. Thus, the patterns 501 for adjustment are notformed in a leading edge portion of the recording medium in theconveying direction, and it is possible to more reliably suppressoccurrence of winding of the recording medium during the fixingprocessing.

The patterns 501 for adjustment are each formed of a plurality of tonepatches (11 tones in FIG. 5 ) in which a tone value of each color isvaried stepwise. The plurality of tone patches are each, for example, asquare shape having a side of about 8 mm, and are arranged in a row inthe conveying direction. In the tone patches of each color, a tone patchfor detecting a texture of the recording medium (that is, a tone patchhaving a tone value of 0) is located at each of both ends of a row ofthe other tone patches. Nine tone patches having evenly distributed tonevalues are arranged so as to be sandwiched between the tone patcheshaving a tone value of 0. In a case where the tone value is representedby a range of from 0 to 255, the patterns 501 for adjustment are eachformed of the tone patches of each color having tone values of 0, 16,32, 64, 86, 104, 128, 176, 224, 255, and 0. The patterns 501 foradjustment are not limited to yellow, magenta, cyan, and black, and maybe formed of respective colors of red, green, and blue and processblack. The size and the tone order are not limited as well.

<Correction of Image Density>

FIG. 6 is a four-quadrant chart for showing how the tones arereproduced. Quadrant I represents a relationship between the density ofan image (original image) to be printed and an input value of image data(density signal) indicating the image. Quadrant II represents aconversion condition (γLUT) for converting the density signal into alaser output signal indicating an amount of laser light output from theexposure device 227. Quadrant III represents tone characteristics(printer characteristics) of the printing apparatus 107 indicating arelationship between the laser output signal and the density (imagedensity) of the image formed on the recording medium. Quadrant IVindicates a relationship between the density of the original image andthe density (image density) of the image formed on the recording medium.That is, the four-quadrant chart represents total tone reproductioncharacteristics of the printing apparatus 107 illustrated in FIG. 1 .

The printing apparatus 107 generates a conversion condition (γLUT) inquadrant II so that the density of the original image and the imagedensity have an ideal relationship (linear relationship). Thus, in acase where a γLUT is generated based on the reading results obtained bythe reading sensors 351 and 353, the CPU 222 obtains tonecharacteristics from the reading results of the patterns 501 foradjustment, and generates a γLUT so that the tone characteristics becomeideal tone characteristics. An image signal having the tonecharacteristics converted by the γLUT is converted into a pulse signalcorresponding to a dot width by a pulse width modulation (PWM) circuitof a laser driver, and is transmitted to the laser driver for drivingand controlling the exposure device 227. In this embodiment, a tonereproduction method based on pulse width modulation is used for all thecolors of yellow, magenta, cyan, and black.

The laser light output from the exposure device 227 is scanned, tothereby form, on the photosensitive drum, an electrostatic latent imagehaving the tones controlled by changing the dot area to havepredetermined tone characteristics. This electrostatic latent image isdeveloped into a toner image, and the toner image is transferred onto arecording medium and fixed to the recording medium, to thereby reproducea tone image.

<Method of Setting Automatic Adjustment>

The image forming apparatus 101 according to this embodiment is capableof setting automatic adjustment for automatically adjusting the imageforming conditions during printing. FIG. 7A to FIG. 7D are explanatoryviews of a setting screen for setting the automatic adjustment. Thesetting screen is displayed on the display 225 by the CPU 222. The usercan set the automatic adjustment from the setting screen through theoperating device 224. The user sets the automatic adjustment beforeinstructing execution of printing.

FIG. 7A is an illustration of an initial screen. In a case where theuser selects a soft key labeled “ADVANCED MODE” from the initial screen,the CPU 222 displays an advanced mode selection screen of FIG. 7B on thedisplay 225. In a case where the user selects a soft key labeled “CLOSE”from the advanced mode selection screen, the CPU 222 displays theinitial screen of FIG. 7A on the display 225. In a case where the userselects a soft key labeled “ADJUST” from the advanced mode selectionscreen, the CPU 222 displays an adjustment mode selection screen of FIG.7C on the display 225.

In a case where the user selects a soft key labeled “REAL TIME” from theadjustment mode selection screen, a real-time mode for adjusting imageforming conditions in real time is set. In the real-time mode, thepatterns 501 for adjustment are formed in a margin area of the recordingmedium on which an image corresponding to a job has been printed. Thus,the image forming conditions are adjusted every time an image is formedin accordance with a job. The CPU 222 notifies the external controller102 that the real-time mode has been set. In a case where a job isstarted, the external controller 102 instructs the CPU 222 to print thepatterns 501 for adjustment in the real-time mode. In a case where theuser selects a soft key labeled “BACK” from the adjustment modeselection screen, the CPU 222 displays the advanced mode selectionscreen of FIG. 7B on the display 225.

In a case where the user selects a soft key labeled “PREDETERMINEDINTERVAL” from the adjustment mode selection screen, the CPU 222displays an adjustment interval setting screen of FIG. 7D on the display225. In a case where the user presses a soft key labeled “OK” afterinputting the number of sheets by a numeric keypad on the adjustmentinterval setting screen, automatic adjustment is enabled. Thus, apredetermined-interval mode and the number of sheets of an adjustmentinterval are set. In the example of FIG. 7D, 200 sheets are set as thenumber of sheets of the adjustment interval. A chart for adjustment iscreated every time an image is formed on the number of sheets ofrecording media set as the adjustment interval. That is, the automaticadjustment is performed for every number of sheets set as the adjustmentinterval, to thereby adjust the image forming conditions. The CPU 222notifies the external controller 102 that the predetermined-intervalmode and the number of sheets of the adjustment interval have been set.In a case where a job is started, the external controller 102 instructsthe CPU 222 to print the patterns 501 for adjustment on the number ofsheets of the adjustment interval. In a case where the user selects asoft key labeled “BACK” from the adjustment interval setting screen, theCPU 222 displays the adjustment mode selection screen of FIG. 7C on thedisplay 225.

For example, in a case in which the number of sheets of the adjustmentinterval is set to 200, in a case where the printing on 1,000 sheets ofrecording media is instructed by a print job, a chart for adjustment iscreated at a printing interval of 200 sheets in thepredetermined-interval mode. In this case, a chart for adjustment iscreated between the 200th page and the 201st page, between the 400thpage and the 401st page, between the 600th page and the 601st page, andbetween the 800th page and the 801st page. That is, the image density iscorrected between the 200th page and the 201st page, between the 400thpage and the 401st page, between the 600th page and the 601st page, andbetween the 800th page and the 801st page, to thereby adjust the imageforming conditions.

<Printing Processing>

FIG. 8 , FIG. 9 , and FIG. 10 are flow charts for illustrating printingprocessing including correction processing for the image density, whichis performed by the image forming apparatus 101 having theabove-mentioned configuration. In this embodiment, in a case where theCPU 222 of the printing apparatus 107 obtains a printing instructionfrom the external controller 102, the CPU 222 determines the γLUT as atarget tone serving as a target value. The CPU 222 forms an imagethrough use of the determined γLUT. Each time the printing on apredetermined number of sheets of recording media is ended duringexecution of a print job, the CPU 222 performs image density correction,and corrects a difference from the target value (target tone) to updatethe γLUT.

The CPU 222 stands by until the CPU 222 receives a print job from theexternal controller 102 (“N” in Step S801). In a case where the CPU 222receives the print job (“Y” in Step S801), the CPU 222 determineswhether or not the predetermined-interval mode is set on the settingscreens exemplified in FIG. 7A to FIG. 7D (Step S802). In a case wherethe predetermined-interval mode is not set (“N” in Step S802), the CPU222 prints an image specified by the print job on the recording medium(Step S803). After the printing, the CPU 222 determines whether or notall the printing processes instructed by the print job have been ended(Step S804). In a case where not all the printing processes have beenended (“N” in Step S804), the CPU 222 repeatedly performs the printingprocessing until all the printing processes instructed by the print jobhave been ended. In a case where all the printing processes have beenended (“Y” in Step S804), the CPU 222 ends the processing.

In a case where the predetermined-interval mode is set (“Y” in StepS802), the CPU 222 sets an image density correction flag to off, andsets a reading failure count to “0” (Step S805). The image densitycorrection flag is a flag to be set to on in a case where the imagedensity correction is determined to be executed by image densitycorrection determining processing, which is described later. The readingfailure count is “0” at the start of a print job. The reading failurecount represents the number of times that the reading of a chart foradjustment has failed during the print job. In a case where the readingfailure count reaches a predetermined number or more, in thisembodiment, “5” or more, the CPU 222 determines that an error hasoccurred because there is a possibility that a failure has occurred inthe CIS 321 or the CIS 322. The failure in reading the chart foradjustment is determined based on, for example, a reading result or adetection result obtained by a sensor for detecting the conveyance ofthe chart for adjustment. The CPU 222 determines that the reading of thechart for adjustment has failed in a case where the reading result ofthe chart for adjustment includes an abnormal value. The CPU 222determines that the reading of the chart for adjustment has failed in acase where a detection timing of the sensor for detecting the conveyanceof the chart for adjustment is later or earlier than predicted.

Subsequently, the CPU 222 executes target tone determining processing,which is described later (Step S806). After the end of the target tonedetermining processing, the CPU 222 sets a count value C of an executioninterval of the image density correction to “0” (that is, clears thecount value C) (Step S807). The CPU 222 determines whether or not theimage density correction flag is set to on (Step S808). In a case wherethe image density correction flag is set to on (“Y” in Step S808), theCPU 222 corrects the image density based on the correctioncharacteristics of the image density (Step S809). After the imagedensity correction, the CPU 222 prints the image specified by the printjob on the recording medium (Step S803). In a case where the imagedensity correction flag is set to off (“N” in Step S808), the CPU 222prints the image specified by the print job on the recording mediumwithout performing the image density correction (Step S803).

After the printing processing, the CPU 222 adds “1” to the count value C(Step S811). The CPU 222 determines whether or not all the printingprocesses instructed by the print job have been ended (Step S812). In acase where all the printing processes have been ended (“Y” in StepS812), the CPU 222 ends the processing. When not the printing processesall have been ended (“N” in Step S812), the CPU 222 determines whetheror not the count value C exceeds the set value of the number of sheetsof the adjustment interval set on the adjustment interval setting screenof FIG. 7D (Step S813).

In a case where the count value C does not exceed the set value (“N” inStep S813), the CPU 222 repeatedly performs Step S808 and the subsequentprocessing steps. In a case where the count value C exceeds the setvalue (“Y” in Step S813), the CPU 222 performs the image densitycorrection determining processing, which is described later (Step S814).After the image density correction determining processing, the CPU 222repeatedly performs Step S807 and the subsequent processing steps.

As described above, the CPU 222 determines the target tone when thepredetermined-interval mode is set, and prints an image on recordingmedia in accordance with a print job while correcting an image densityeach time the count value C exceeds the set value. After the end of theimage formation on the number of sheets of recording media as instructedby the print job, the CPU 222 ends the processing corresponding to theprint job. Even when an error occurs in the target tone determiningprocessing of Step S806 or the image density correction determiningprocessing of Step S814, the CPU 222 ends the processing correspondingto the print job.

FIG. 9 is a flow chart for illustrating the target tone determiningprocessing of Step S806.

The CPU 222 examines, based on a print job obtained from the externalcontroller 102, a type of recording media being used for the print joband an image forming mode (duplex printing or single-sided printing)(Step S901). The CPU 222 conveys one of the recording media being usedfor the print job, and creates a chart for adjustment (Step S902). In acase of the single-sided printing, the CPU 222 creates a chart foradjustment by forming the patterns 501 for adjustment for tonecorrection on one side of the recording medium. In a case of the duplexprinting, the CPU 222 creates a chart for adjustment by forming thepatterns 501 for adjustment for tone correction on both sides of therecording medium. The CPU 222 reads the created chart for adjustment bythe CISs 321 and 322 (Step S903). The CPU 222 determines success orfailure of the reading processing based on a reading result of thepatterns 501 for adjustment which has been obtained by each of the CIS321 and 322 (Step S904). For example, the CPU 222 determines that thereading processing has failed in a case where the reading resultincludes an abnormal value.

In a case where the reading processing is successful (“Y” in Step S904),the CPU 222 determines the target tone serving as the target value basedon the reading result of the patterns 501 for adjustment which has beenobtained by each of the CISs 321 and 322 (Step S905). The CPU 222, whichhas determined the target tone, ends the target tone determiningprocessing, and the process advances to the processing step of StepS807.

In a case where the reading processing fails (“N” in Step S904), the CPU222 adds “1” to the reading failure count (Step S906). The CPU 222determines whether or not the reading failure count is the predeterminednumber or more. In this embodiment, the CPU 222 determines whether ornot the reading failure count is “5” or more (Step S907). In a casewhere the reading failure count is smaller than “5” (“N” in Step S907),the process returns to the processing step of Step S902, and the CPU 222creates a chart for adjustment again to attempt to determine the targettone. In a case where the reading failure count is “5” or more (“Y” inStep S907), the CPU 222 determines that there is a possibility that afailure has occurred in the CIS 321 or the CIS 322. Therefore, the CPU222 stops the operation due to an error (Step S908), and ends the printjob.

As described above, in the target tone determining processing, in a casewhere the reading of the patterns 501 for adjustment fails, a chart foradjustment is repeatedly created and read until it is determined thatthere is a possibility that a failure has occurred in the CIS 321 or theCIS 322. In a case where the target tone is determined while a chart foradjustment is created and read a predetermined number of times, theimage formation corresponding to the print job keeps being performed asit is. In a case where the reading of the patterns 501 for adjustmenthas failed a predetermined number of times in a row, the print job endsdue to an error. Once the target tone is determined, the image qualityis maintained from the beginning of the print job.

FIG. 10 is a flow chart for illustrating the image density correctiondetermining processing of Step S814.

The CPU 222 conveys one of the recording media being used for the printjob, and creates a chart for adjustment by forming the patterns 501 foradjustment for tone correction on this recording medium (Step S1001).The CPU 222 reads the formed chart for adjustment by each of the CISs321 and 322 (Step S1002). The CPU 222 determines the success or failureof the reading processing based on the reading result of the patterns501 for adjustment which has been obtained by each of the CISs 321 and322 (Step S1003). For example, the CPU 222 determines that the readingprocessing has failed in a case where the reading result includes anabnormal value. In a case where the CIS 321 reads the chart foradjustment, the CPU 222 determines that the reading processing hasfailed in a case where a brightness value of the read image relating tothe chart for adjustment which has been output from the CIS 321 fallsout of an allowable range. In the same manner, in a case where the CIS322 reads the chart for adjustment, the CPU 222 determines that thereading processing has failed in a case where a brightness value of theread image relating to the chart for adjustment which has been outputfrom the CIS 322 falls out of the allowable range.

In a case where the reading processing is successful (“Y” in StepS1003), the CPU 222 compares the reading result of the patterns 501 foradjustment which has been obtained by each of the CISs 321 and 322 andthe target tone to each other to determine the correctioncharacteristics of the image density (Step S1004). The CPU 222 furthersets the image density correction flag to on (Step S1005). The CPU 222,which has set the image density correction flag to on, ends the imagedensity correction determining processing, and the process advances tothe processing step of Step S807.

In a case where the reading processing fails (“N” in Step S1003), theCPU 222 adds “1” to the reading failure count (Step S1006). The CPU 222determines whether or not the reading failure count is the predeterminednumber or more. In this embodiment, the CPU 222 determines whether ornot the reading failure count is “5” or more (Step S1007). Once theprint job is started, the reading failure count does not become “0”except that the reading failure count is cleared in the processing stepof Step S805. Thus, at the stage of the processing step of Step S1007,the reading failure count is obtained by adding “1” to the number oftimes that the reading has failed in the target tone determiningprocessing. That is, it is determined in the processing step of StepS1007 whether or not a total reading failure count since the start ofthe print job is the predetermined number or more.

In a case where the reading failure count is smaller than “5” (“N” inStep S1007), the CPU 222 ends the image density correction determiningprocessing, and the process advances to the processing step of StepS807. In a case where the reading failure count is “5” or more (“Y” inStep S1007), the CPU 222 determines that there is a possibility that afailure has occurred in the CIS 321 or the CIS 322. Therefore, the CPU222 stops the operation due to an error (Step S1008), and ends the printjob.

As described above, in the image density correction determiningprocessing, even when the reading of the patterns 501 for adjustment hasfailed, the reading of the patterns 501 for adjustment is not repeatedlyperformed. Thus, productivity is prevented from decreasing by the imagedensity correction determining processing. In a case where the operationis stopped due to an error in the target tone determining processing andthe image density correction determining processing, the CPU 222notifies the user that the job has been stopped due to an error throughuse of the display 225. The CPU 222 thus prompts the user to handle thesituation.

In the image forming apparatus 101 according to this embodiment, thetarget tone is determined at the start of a print job, and the imageforming conditions are adjusted even when an image is continuouslyformed by the print job. With the setting of the target tone performedat the start of a print job, even in the case of a print job forperforming printing continuously, the image quality is maintained froman image formed on the first recording medium, to thereby guaranteestability in color tint. Further, in the image density correctiondetermining processing during the print job, the processing is notrepeatedly performed, and hence the productivity is guaranteed. As theprocessing in this embodiment, it is possible to employ any processingthat maintains the image quality by reading an image for adjustmentformed on a recording medium and adjusting the image forming conditionsbased on the reading result of the image for adjustment. The effects ofthis embodiment can also be obtained in the same manner for suchprocessing. As described above, according to the embodiment of thepresent disclosure, it is possible to maintain the image quality whilesuppressing a decrease in productivity.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2021-089870, filed May 28, 2021, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An image forming apparatus comprising: an imageforming unit configured to form an image on a recording medium based onan image forming condition; an image reader configured to read an imagefor adjustment of the image forming condition, which is formed on therecording medium; and a controller configured to: control the imageforming unit to form images for adjustment; control the image reader toread the images for adjustment; determine a target data based on areading result of a first image included in reading results of theimages for adjustment; adjust the image forming condition, duringexecution of a job in which the image forming unit forms a plurality ofimages on a plurality of recording mediums, based on the target data anda reading result of second image included in the reading results of theimages for adjustment; control the image forming unit to form the firstimage again during execution of the job, in a case where the imagereader fails to read the first image during execution of the job; andavoid adjust the image forming condition based on the reading result ofthe second image during execution of the job, in a case where the imagereader fails to read the second image during execution of the job. 2.The image forming apparatus according to claim 1, wherein the controlleris configured to control the image forming unit to form the first imagebefore the second image is to be formed.
 3. The image forming apparatusaccording to claim 1, wherein the controller is configured to controlthe image forming unit to form the second image the image formingcondition each time the image forming unit ends forming an image on apredetermined number of sheets of recording media.
 4. The image formingapparatus according to claim 1, wherein the controller is configured todetermine that a possibility that a failure has occurred in the imagereader exists in a case where the image reader fails to read the firstimage a predetermined number of times.
 5. The image forming apparatusaccording to claim 1, wherein the controller is configured to determinethat a possibility that a failure has occurred in the image readerexists in a case where a number of times the image reader fails to readthe second image is equal to or larger than a predetermined number oftimes.
 6. The image forming apparatus according to claim 4, wherein thecontroller is configured to end the job when it has been determined thata possibility that a failure has occurred in the image reader exists. 7.The image forming apparatus according to claim 4, wherein the controlleris configured to notify that the job has been stopped due to an errorwhen it has been determined that a possibility that a failure hasoccurred in the image reader exists.